A conventional polarizing plate generally used for LCDs includes a polarizer and a transparent protective film bonded to both sides of the polarizer with an adhesive. A polyvinyl alcohol polarizer is generally used as the polarizer, which is produced by adsorbing iodine into polyvinyl alcohol and orienting it by stretching. Triacetylcellulose is generally used for the transparent protective film. In general, the polarizing plate is used in the form of a pressure-sensitive adhesive attached polarizing plate in which an acrylic pressure-sensitive adhesive layer made of an acrylic pressure-sensitive adhesive is laminated for stacking on a liquid crystal cell or the like.
In recent years, wide viewing angle and high contrast have been demanded. Therefore, a polarizing plate and a retardation layer (a birefringent layer) are laminated in such a manner that the retardation properties of the retardation layer can match the retardation properties of a liquid crystal cell during black viewing, so that high display quality has become possible by achieving wide viewing angle and high contrast. For example, a retardation layer using a discotic liquid crystal is laminated on a polarizing plate so that viewing angle can be significantly increased because of the oblique viewing angle compensation of a TN liquid crystal.
However, a retardation layer-attached polarizing plate having a laminated retardation layer using the discotic liquid crystal has a problem in which the polarizer can experience the effect of environmental change, such as dimensional shrinkage, so that the retardation of the retardation layer can be changed, the contrast can be reduced, or unevenness of in-plane black brightness can be developed, so that visibility can be significantly reduced.
Against such a problem, some techniques are proposed, which include reducing the thickness of a base film on which a discotic liquid crystal retardation layer is laminated (Patent Literature 1), using a material with a small photoelastic coefficient as the base film (Patent Literature 2), reducing the thermal expansion coefficient of a cellulose acetate film for use as the base film (Patent Literature 3), and increasing the stress relaxation properties of a pressure-sensitive adhesive layer (Patent Literature 4).
There is also proposed a method in which an adhesive containing an acetoacetyl group-containing polyvinyl alcohol resin and a crosslinking agent such as glyoxal is used between a polarizer and a transparent protective film in a polarizing plate so that the water resistance of the adhesive interface can be improved, and defects such as delamination (peeling of the edge portion of a transparent protective film from a polarizer) in severe high-temperature and humid environment can be avoided (Patent Literature 5).
Even if the techniques for improving durability are combined as described above to form the retardation layer-attached polarizing plate, however, in the above-mentioned environment, the peripheral portion of the polarizing plate can form peripheral unevenness due to depolarization and can have significantly reduced polarization performance to fail to maintain the visibility.
For on-vehicle applications and the like, it is also required that the visibility should be maintained even in a test simulating a very severe environment, such as a high temperature of 100° C., high temperature and high humidity of 60° C./95% RH, and a thermal shock test including cycles of the conditions of −40° C. and 80° C. However, pressure-sensitive adhesive layers with good stress relaxation properties generally have poor adhesion so that they cannot follow the sudden dimensional-shrinkage behavior of the polarizing plate in a thermal shock test and can suffer from appearance defects such as peeling and foaming.    Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 2004-163606    Patent Literature 2: JP-A No. 2001-100036    Patent Literature 3: JP-A No. 2003-55477    Patent Literature 4: JP-A No. 07-198945    Patent Literature 5: JP-A No. 2005-3884